A computer system is capable of employing a variety of data protection technologies such as snapshot and mirroring functionality. A snapshot is not a full copy of a production volume. Rather, a snapshot includes only original portions of the production volume which have changed since the snapshot was taken, i.e., Copy on First Write (CoFW) data. On the other hand, a mirror is a full copy of a production volume, i.e., a byte-by-byte real time copy of the production volume.
Examples of snapshot-related products include SnapSure™ and SnapView™ both of which are provided by EMC Corporation of Hopkinton, Mass. An example of a mirroring product is MirrorView™ which is also provided by EMC Corporation of Hopkinton, Mass.
In connection with conventional snapshots, suppose that an original data block of a particular production volume requires updating on a computer system. Along these lines, when the processor of the computer system receives an instruction to modify the original data block of the particular production volume (e.g., a write instruction, a read-modify-write instruction, etc.), the processor allocates memory and then reads the original data block of the particular production volume (as CoFW data) from disk synchronously into the allocated memory. Such reading of the original data block from disk takes place even if the original data block already resides in the buffer cache of the computer system due to an earlier read IO.